Light-emitting device having a roughened surface with different topographies

ABSTRACT

This invention provides an optoelectronic semiconductor device having a rough surface and the manufacturing method thereof. The optoelectronic semiconductor device comprises a semiconductor stack having a rough surface and an electrode layer overlaying the semiconductor stack. The rough surface comprises a first region having a first topography and a second region having a second topography. The method comprises the steps of forming a semiconductor stack on a substrate, forming an electrode layer on the semiconductor stack, thermal treating the semiconductor stack, and wet etching the surface of the semiconductor stack to form a rough surface.

REFERENCE TO RELATED APPLICATION

The present application claims the right of priority based on TaiwanApplication Ser. No. 096131320, filed Aug. 23, 2007, the disclosure ofwhich is incorporated herein by reference in its entirety.

TECHNICAL FIELD

This invention relates to a semiconductor optoelectronic device having arough surface and the manufacturing method thereof.

BACKGROUND OF THE DISCLOSURE

Surface roughening is one of the efficient ways to improve lightextraction efficiency of a light-emitting device. Roughening thesubstrate or the upmost semiconductor layer into irregularprotrusions/depressions to scatter incident light impinging on theroughened surface is an example to improve light extraction efficiency.Roughening surface can be achieved by known processes like mechanicallypolishing or reactive-ion-etching (RIE). Another feasible way isperformed by wet etching the wafer immersed in an etching solution forcertain duration. The surface is roughened by different etching rates ofthe etching solution versus different exposed crystal planes of thesurface. The roughened surface of the light-emitting device, as shown inFIG. 1, is formed by wet etching. The light-emitting device comprises agrowth substrate 11, an n-type semiconductor layer 12, an active layer13, a p-type semiconductor 14, a p-side conductive pad, and an n-sideconductive pad. The surface of the p-type semiconductor layer 14 iswet-etched to form a roughened surface. An undercut 17 is formed due tolateral etching in the border between the p-side conductive pad 16 andthe p-type semiconductor layer 14. The contact area between the p-sideconductive pad 16 and the p-type semiconductor layer 14 is thereforereduced such that the device reliability is easily failed or the p-sideconductive pad 16 is easily peeled off by the stress. Besides, theuniformity of the roughened surface formed by the conventional wetetching method is not good enough to keep the product stable.

Another conventional way to prevent the light-emitting device fromreliability failure or pad peeling is to form the roughened surfacebefore forming the conductive pad, but the contact resistance betweenthe conductive pad and the roughened surface of the underlying layerbecomes high and therefore downgrade the device performance. Besides,the resulted surface of the conductive pad is uneven and thereforeobstructs the wire-bonding yield.

SUMMARY OF THE DISCLOSURE

One aspect of the present invention is to provide an optoelectronicsemiconductor device comprising a substrate; a semiconductor stackfurther comprising a first semiconductor layer of a first conductivity,an active layer, and a second semiconductor layer of a secondconductivity; and an electrode layer formed on the second semiconductorlayer; wherein the first and/or second semiconductor layer having arough surface comprising a first region having a first topography and asecond region having a second topography.

Another aspect of the present invention is to provide a method forforming a rough surface on a semiconductor layer of an optoelectronicsemiconductor device. The method comprises the steps of forming asemiconductor stack on a substrate; forming an electrode layer on thesemiconductor stack; heat treating the semiconductor stack and theelectrode layer; and wet etching the surface of the semiconductor stackto form a rough surface.

The optoelectronic semiconductor device comprises light-emitting deviceor photovoltaic device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing a light-emitting device accordingto a conventional structure.

FIG. 2A to FIG. 2B are schematic diagrams showing one embodiment of alight-emitting device in accordance with the present invention.

FIG. 2C is a schematic diagram showing the top view of thelight-emitting device in FIG. 2A or FIG. 2B.

FIG. 3A is an SEM picture showing the first topography of the roughsurface formed in accordance with the present invention.

FIG. 3B is an SEM picture showing the second topography of the roughsurface formed in accordance with the present invention.

FIG. 4 is a flow chart showing the manufacturing method in accordancewith the present invention.

FIG. 5A to FIG. 5C are schematic diagrams showing a light-emittingdevice comprising a bonding structure in accordance with the presentinvention.

FIG. 6 is a schematic diagram showing a light-emitting device comprisinga lateral structure in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 2A to FIG. 2C show a light-emitting device 2 in accordance with thepresent invention. FIG. 2C is a top view of the light-emitting device 2,and FIG. 2A and FIG. 2B are the cross-section views along with AA′ andBB′ respectively. As shown in FIG. 2A and FIG. 2B, the light-emittingdevice 2 comprises a substrate 21 having a top surface and a bottomsurface; a first semiconductor layer 22 of a first conductivityoverlaying the substrate; an active layer 23 overlaying the firstsemiconductor layer 22; a second semiconductor layer 24 of a secondconductivity comprising a rough surface overlaying the active layer 23;an extended electrode layer 25 overlaying the second semiconductor layer24; a first conductive pad 26 overlaying a portion of the extendedelectrode layer 25 and a portion of the second semiconductor layer 24;and a second conductive pad 27 underlying the bottom surface of thesubstrate 21. The material of the first semiconductor layer 22, theactive layer 23, or the second semiconductor layer 24 comprises n-typeor p-type Al_(p)Ga_(q)In_((1-p-q))P or Al_(x)In_(y)Ga_((1-x-y))N (0≦p,q, x, y≦1; (p+q)≦1; (x+y)≦1). The first semiconductor layer 22 comprisesa first conductivity type cladding layer, and the second semiconductorlayer 24 comprises a second conductivity type cladding layer. Theextended electrode layer 25 is a current spreading layer having apattern extended toward the surroundings of the light-emitting devicefor spreading current as shown in FIG. 2C. The first conductive pad 26is a bonding pad covering and electrically coupled to a portion of theextended electrode layer 25. The material of the extended electrodelayer 25 comprises single or multilayer of metal or metal alloy such asGe/Au. The material of the conductive pad 26 comprises multilayer ofmetal such as Cr/Au. In one embodiment, the light-emitting device 2further comprises an ohmic contact layer 28 interposed between thesecond semiconductor layer 24 and the extended electrode layer 25. Theohmic contact layer 28 comprises a semiconductor layer with a higherdoping concentration than that of the second semiconductor layer 24,such as GaAs having Si-doping concentration higher than 10¹⁸cm⁻³. Theconductivity type of the ohmic contact layer 28 can be the same as ordifferent to the second semiconductor layer 24 and form an ohmic contactwith the second semiconductor layer 24. In a preferred embodiment, theohmic contact layer 28 is formed only under the region covered by theextended electrode layer 25. The first conductivity type comprisesn-type or p-type, and the second conductivity type is different from thefirst conductivity type.

The rough surface comprises a first region 241 having a first roughtopography and a second region 242 having a second rough topography. Thefirst region and the second region comprise a plurality of depressionsand protrusions. The dimension of the first rough topography is smallerthan that of the second rough topography. In an embodiment of thepresent invention, the distance between the neighboring depressions orthe distance between the neighboring protrusions of the first roughtopography is around 0.1 to 0.5 micron. The depth of at least one of thedepressions or the height of at least one protrusion of the first roughtopography is around 0.1 to 0.5 micron. The distance between theneighboring depressions or the distance between the neighboringprotrusions of the second rough topography is around 1 to 10 microns.The depth of at least one of the depressions or the height of at leastone of the protrusions of the second rough topography is around 0.5 to 2microns. The first rough topography as shown in FIG. 3A is a randomlyrough surface having a plurality of depressions and protrusions. Thesecond rough topography as shown in FIG. 3B is a wave-shape surface. Thesecond region 242 having the second topography is adjacent to andsurrounds the extended electrode layer 25, and therefore separating theextended electrode layer 25 from the first region 241 having the firstrough topography. The level, i.e. the average altitude of the surface,of the second region 242 is about 0.5 to 2 microns lower than that ofthe first region 241. The cross-sectional shape of the second region 242is a curve such that the interface between the extended electrode layer25 and the second region 242 is outward oblique from the extendedelectrode layer 25 to prevent from undercut and further improve thereliability of the device and the peeling-off issue of the electrodelayer.

FIG. 4 discloses a manufacturing method for forming the above-mentionedlight-emitting diode 2. The method comprises the steps of:

-   -   1. providing a growth substrate 21;    -   2. forming a first semiconductor layer 22, an active layer, and        a second semiconductor layer 24 sequentially on the growth        substrate;    -   3. forming an extended electrode layer 25 on the second        semiconductor layer 24;    -   4. forming a first conductive pad 26 on a portion of the        extended electrode layer 25 and the second semiconductor layer        24;    -   5. proceeding a thermal treatment step, such as rapid thermal        annealing (RTA);    -   6. wet etching the second semiconductor layer 24 by an etching        solution comprising HF,HNO₃,CH₃COOH, and iodine under a low        temperature condition from room temperature to 60° C. to form a        rough surface thereon, wherein the features of the rough surface        is described in the previous embodiments, such as FIG. 3A and        FIG. 3B;    -   7. forming a second conductive pad 27 on the other side of the        substrate 21.

The structure formed by the method is shown in FIG. 2A or FIG. 2B.

FIG. 5A shows another embodiment of the present invention. Thelight-emitting device 5 a as shown in FIG. 5A is similar to thelight-emitting device 2. The distinction is that the substrate 51 of thelight-emitting device 5 a is a conductive substrate. The substrate 51can also be a transparent or opaque conductive substrate. It is alsopreferred that the substrate is a conductive substrate comprising amaterial having high thermal conductivity not lower than 100 W/cm·° C.,such as Si, Cu, or diamond. The conductive substrate 51 is coupled tothe first semiconductor layer 22 by a conductive connecting layer 52.The conductive connecting layer 52 comprises a transparent conductivelayer or a conductive adhesive layer. The material of the transparentconductive layer comprises transparent conductive oxide, such as indiumtin oxide (ITO), zinc oxide (ZnO), or thin metal. The material of theconductive adhesive layer comprises silver paste or solder metal. Thelight-emitting device 5 a further comprises a reflecting layer 53 formedbetween the conductive connecting layer 52 and the first semiconductorlayer 22 for reflecting the light emitted from the active layer 23 andpreventing from being absorbed by the conductive substrate 51 if theconductive substrate 51 is opaque.

The manufacturing method for forming the light-emitting device 5 acomprises the steps of:

-   -   1. providing a growth substrate (not shown);    -   2. forming a first semiconductor layer 22, an active layer 23,        and a second semiconductor layer 24 sequentially on the growth        substrate;    -   3. bonding a temporary substrate (not shown) to the second        semiconductor layer 24;    -   4. removing the growth substrate to expose one surface of the        first semiconductor layer 22;    -   5. forming a reflecting layer 53 on the exposed surface of the        first semiconductor layer 22;    -   6. forming a conductive connecting layer 52 on a conductive        substrate 51;    -   7. bonding the conductive substrate 51 with the conductive        connecting layer 52 to the reflecting layer 53;    -   8. removing the temporary substrate to expose one surface of the        second semiconductor layer 24    -   9. forming an extended electrode layer 25 on the exposed surface        of the second semiconductor layer 24;    -   10. forming a first conductive pad 26 on a portion of the        extended electrode layer 25 and the second semiconductor layer        24;    -   11. proceeding a thermal treatment step, such as rapid thermal        annealing (RTA);    -   12. wet etching the second semiconductor layer 24 to form a        rough surface thereon, wherein the features of the rough surface        is described in the previous embodiments, such as FIG. 3A and        FIG. 3B;    -   13. forming a second conductive pad 27 on the other side of the        conductive substrate 51.

FIG. 5B shows another embodiment of the present invention. Thelight-emitting device 5 b as shown in FIG. 5B is similar to thelight-emitting device 5 a mentioned above. The distinction is that therough surface is formed on the first semiconductor layer 22.

The manufacturing method for forming the light-emitting device 5 bcomprises the steps of:

-   -   1. providing a growth substrate (not shown);    -   2. forming a first semiconductor layer 22, an active layer 23,        and a second semiconductor layer 24 sequentially on the growth        substrate;    -   3. forming a reflecting layer 53 on the second semiconductor        layer 24;    -   4. forming a conductive connecting layer 52 on a conductive        substrate 51;    -   5. bonding the conductive substrate 51 with the conductive        connecting layer 52 to the reflecting layer 53;    -   6. removing the growth substrate to expose one surface of the        first semiconductor layer 22;    -   7. forming an extended electrode layer 25 on the exposed surface        of the first semiconductor layer 22;    -   8. forming a first conductive pad 26 on a portion of the        extended electrode layer 25 and the first semiconductor layer        22;    -   9. proceeding a thermal treatment step, such as rapid thermal        annealing (RTA);    -   10. wet etching the first semiconductor layer 22 to form a rough        surface thereon, wherein the features of the rough surface is        described in the previous embodiments, such as FIG. 3A and FIG.        3B;    -   11. forming a second conductive pad 27 on the other side of the        conductive substrate 51.

FIG. 5C shows another embodiment of the present invention. Thedistinction between the light-emitting device 5 c as shown in FIG. 5Cand the above-mentioned embodiment is that the rough surface is formedinside the light-emitting device 5 c instead of on the outer surface ofthe light-emitting device.

The manufacturing method for forming the light-emitting device 5 ccomprises the steps of:

-   -   1. providing a growth substrate (not shown);    -   2. forming a first semiconductor layer 22, an active layer 23,        and a second semiconductor layer 24 sequentially on the growth        substrate;    -   3. forming an extended electrode layer 25 on the second        semiconductor layer 24;    -   4. proceeding a thermal treatment step, such as rapid thermal        annealing (RTA);    -   5. wet etching the second semiconductor layer 24 to form a rough        surface thereon, wherein the features of the rough surface is        described in the previous embodiments, such as FIG. 3A and FIG.        3B;    -   6. forming a reflecting layer 53 on a conductive substrate 51;    -   7. forming a conductive connecting layer 52 on the reflecting        layer 53;    -   8. bonding the extended electrode layer 25 and the second        semiconductor layer 24 to the reflecting layer 53 by the        conductive connecting layer 52;    -   9. removing the growth substrate to expose one surface of the        first semiconductor layer 22;    -   10. forming a first conductive pad 26 on a portion of the        exposed surface of the first semiconductor layer 22;    -   11. forming a second conductive pad 27 on the other side of the        conductive substrate 51.

FIG. 6 shows a light-emitting device having a lateral structure asanother embodiment of the present invention. The light-emitting device 6and the light-emitting device 5 c each comprises a rough surface insidethe device. The distinction is that the light-emitting device 6 furthercomprises a transparent conductive layer 63 for electrically couplingthe first conductive pad 26 to the second conductive pad 27 and bondingto a transparent substrate 61 by a transparent adhesive layer 62. Atleast one of the transparent adhesive layer 62 and the transparentsubstrate 61 comprises an insulating layer or an insulating structurefor electrically isolating the transparent substrate 61 from thetransparent conductive layer 63, such as forming an insulating layer ona transparent conductive substrate. The material of the transparentconductive layer 63 comprises indium tin oxide (ITO), zinc oxide (ZnO)or thin metal. The material of the transparent adhesive layer 62comprises polyimide (PI), benzocyclobutene (BCB), perfluorocyclobutane(PFCB), epoxy resin, or silicone. The material of the transparentsubstrate 61 comprises sapphire, glass GaP, SiC, or CVD diamond. Thelight-emitting device 6 comprises a transparent bonding structure and atransparent substrate to be capable of extracting light from thesubstrate, and then improve the light extraction efficiency.

The manufacturing method for forming the light-emitting device 6comprises the steps of:

-   -   1. providing a growth substrate (not shown);    -   2. forming a first semiconductor layer 22, an active layer 23,        and a second semiconductor layer 24 sequentially on the growth        substrate;    -   3. forming an extended electrode layer 25 on the second        semiconductor layer 24;    -   4. proceeding a thermal treatment step, such as rapid thermal        annealing (RTA);    -   5. wet etching the second semiconductor layer 24 to form a rough        surface thereon, wherein the features of the rough surface is        described in the previous embodiments, such as FIG. 3A and FIG.        3B;    -   6. forming a transparent conductive layer 63 the extended        electrode layer 25 and the second semiconductor layer 24;    -   7. forming a transparent adhesive layer 62 on a transparent        substrate 61;    -   8. bonding the transparent conductive layer 63 to the        transparent substrate 61 by the transparent adhesive layer 62;    -   9. removing the growth substrate to expose one surface of the        first semiconductor layer 22;    -   10. removing a part of the first semiconductor layer 22, the        active layer 23, the second semiconductor layer 24, and the        transparent conductive layer 63 to expose a portion of the        transparent conductive layer 63;    -   11. forming a first conductive pad 26 on the first semiconductor        layer 22;    -   12. forming a second conductive pad 27 on the exposed portion of        the transparent conductive layer 63.

Another alternative embodiment for step 10 to step 12 of the method forforming the light-emitting device 6 is to remove a part of the firstsemiconductor layer 22, the active layer 23, the second semiconductorlayer 24 to expose a portion of the second semiconductor layer 24, andform the second conductive pad 27 on the exposed portion of the secondsemiconductor layer 24.

According to the various embodiments described as above, it is stillunder the scope of the present invention to form the featured roughsurface on both of the first semiconductor layer and the secondsemiconductor layer to further enhance the light extraction efficiency.

It should be noted that the proposed various embodiments are not for thepurpose to limit the scope of the invention. Any possible modificationswithout departing from the spirit of the invention may be made andshould be covered by the invention.

1. An optoelectronic semiconductor device comprising: a substrate; asemiconductor stack having a rough surface; a transparent adhesive layerbetween the semiconductor stack and the substrate; and an electrodelayer overlaying the semiconductor stack; wherein the rough surfacecomprises a first region having a first rough topography and a secondregion having a second rough topography different from the first roughtopography.
 2. The optoelectronic semiconductor device according toclaim 1, wherein the second region is adjacent to the electrode layer.3. The optoelectronic semiconductor device according to claim 2, whereinthe second region surrounds the electrode layer.
 4. The optoelectronicsemiconductor device according to claim 1, wherein the level of thesecond region is lower than the level of the first region.
 5. Theoptoelectronic semiconductor device according to claim 1, wherein thedimension of the second region is larger than the dimension of the firstregion.
 6. The optoelectronic semiconductor device according to claim 1,wherein the electrode layer comprises an extended portion.
 7. Theoptoelectronic semiconductor device according to claim 6, wherein thesecond region is adjacent to the extended portion.
 8. The optoelectronicsemiconductor device according to claim 1, further comprising an ohmiccontact layer formed between the electrode layer and the semiconductorstack.
 9. The optoelectronic semiconductor device according to claim 1,wherein the first rough topography and/or the second rough topography isa random rough surface.
 10. The optoelectronic semiconductor deviceaccording to claim 1, wherein the electrode layer comprises Ge/Au. 11.The optoelectronic semiconductor device according to claim 1, whereinthe semiconductor stack comprises GaP-based or GaN-based semiconductormaterial.
 12. The optoelectronic semiconductor device according to claim1, wherein the transparent adhesive layer is non-conductive.
 13. Anoptoelectronic semiconductor device comprising: a substrate; asemiconductor stack having a rough surface; a conductive adhesive layerbetween the semiconductor stack and the substrate; and an electrodelayer overlaying the semiconductor stack; wherein the rough surfacecomprises a first region having a first rough topography and a secondregion having a second rough topography different from the first roughtopography.
 14. The optoelectronic semiconductor device according toclaim 13, wherein the conductive adhesive layer comprises silver pasteor solder metal.
 15. The optoelectronic semiconductor device accordingto claim 13, wherein the second region is adjacent to the electrodelayer.
 16. The optoelectronic semiconductor device according to claim15, wherein the second region surrounds the electrode layer.
 17. Theoptoelectronic semiconductor device according to claim 13, wherein thelevel of the second region is lower than the level of the first region.18. The optoelectronic semiconductor device according to claim 13,wherein the dimension of the second region is larger than the dimensionof the first region.
 19. The optoelectronic semiconductor deviceaccording to claim 13, wherein the electrode layer comprises an extendedportion.
 20. The optoelectronic semiconductor device according to claim19, wherein the second region is adjacent to the extended portion. 21.The optoelectronic semiconductor device according to claim 13, furthercomprising an ohmic contact layer formed between the electrode layer andthe semiconductor stack.
 22. The optoelectronic semiconductor deviceaccording to claim 13, wherein the first rough topography and/or thesecond rough topography is a random rough surface.
 23. Theoptoelectronic semiconductor device according to claim 13, wherein theelectrode layer comprises Ge/Au.
 24. The optoelectronic semiconductordevice according to claim 13, wherein the semiconductor stack comprisesGaP-based or GaN-based semiconductor material.